Ceramic binaural phonograph pickup



1 J. D. HEIBEL 2,947,821

CERAMI C BINAURAL PHONOGRAPH PICKUP Filed April 21, 1958 I i3 Z5 Z4 MFIG. 3

INVENTOR.

FIG-5 MQHM United States Patent O CERAMIC BINAURAL PHONOGRAPH PICKUPJerome D. Heihel, Erie, Pa., assignor to Eric Resistor Corporation,Erie, Pa., a corporation of Pennsylvania Filed Apr. 21,1958, Ser. No.730,006 9 Claims. (Cl. 179-10041) This invention is a piezoelectricelement having separate outputs in response to stress in directions atright angles to each other. One use of such elements is in phonographpickup cartridges for playing single groove binaural records. In suchrecords, a needle tracking the record groove is moved simultaneously intwo directions at right angles to each other, the needle excursion ineach direction corresponding to the output of one of the two binauralchannels. When the element is used in a binaural phonograph pickup, theoutput for each channel appears between a single electrode and ground.

In the drawings, Fig. 1 is a diagrammatic side elevation of a binauralpickup; Fig. 2 is a section on line 2-2 of Fig. 1; Fig. 3 is a diagramof the record groove; Fig. 4 is a circuit diagram; and Fig. 5 is acircuit diagram for another pickup.

The phonograph pickup is intended for single groove binaural recordsWhere the inputs from two binaural microphones are cut in the groove atright angles to each other. For example, the output of the leftmicrophone might cause the record cutter to have a lateral excursion inthe groove while the output from the right microphone might cause therecord cutter to have a hill and dale excursion. In another system, bothmicrophones cause the record-cutter to have excursions along planesinclined 45 degrees to the record surface and 90 degrees to each other.This latter system is diagrammatically illustrated in Fig. 3 where therecord surface is designated as 23, the record groove as 24, and therecord cutter as 25. One of the binaural channels causes excursion ofthe cutter in the direction of arrow 26 while the other of the binauralchannels causes excursion of the cutter in the direction of the arrow27. In playing the record, the needle follows the record groove andduplicates the excursion of the record cutter.

The pickup has a piezoelectric element 1 of one of the polarizableceramics such as barium titanate having one end fixed in a stationarysupport by a rubber bushing 2 and having the other end fixed in a socket3 in a chuck 4 for a needle point 5. The element may be secured in thesocket 3 bycementing and the needle 5 may likewise be secured in thechuck by cementing, thereby producing a rigid assembly.

The piezoelectric element consists of a bar of ceramic having fourlongitudinally extending electrodes symmetrically spaced about itslongitudinal axis. The shape of the bar should be such that itsstiffness is the same in all directions radial to its longitudinal axis.Among such shapes are bars of square or circular cross section or of thecross shape illustrated where the bar has four longitudinally extendingradial flanges or ribs 6 spaced 90 degrees from each other.Longitudinally extending electrodes 7, 8, 9 and 10 are coated on theceramic between adjacent flanges resulting in diametrically opposedpairs of electrodes with each pair centered on an axis 90 degrees fromthe other. For example, the electrodes 7 and 9 are opposite each otherand are centered on an axis 11 2,947,821 Patented Aug. 2, 1960 to theelectrode 8 while the arrows 14, 15 and 16 extend from the electrode 9through electrodes 10 and 7 to the electrode 8. The polarization couldbe described as directly between adjacent electrodes 8 and 9 and inseries from electrode 9 successively through electrodes 10 and 7 toelectrode 8. The degree of polarization is the same between any twoadjacent electrodes in order that the piezoelectric properties maymatch. This polarization may be obtained by first connecting electrodes10 and 8 together, and 9 and 7 together, and then applying polarizingvoltage between 7 and 8 to polarize all four legs 6 equally, withdirection of polarization pointing from 7 to 8 (16), 9 to 8 (13), 9 to10 (14), and 7 to 10 (opposite to 15). It is now necessary to reversethe polarization from 7 to 10. This may be accomplished by connectingelectrodes 7 and 8 and 9 and 10, then applying polarizing voltagebetween 7 and 10 in such a direction as to reverse the polarizationpreviously established across 7 and 10. This applies voltage across 8and 9 in the same direction as previously, and if first polarization ismade complete, no further change in polarization of leg corresponding toarrow 13 will take place, and all polarizations will be equal.

In the assembly, the piezoelectric element is oriented so that theneedle 5 is directly in line with one of the longitudinal flanges 6. Theassembly is then located in the bushing support 2 so that the needle isperpendicular to the record surface. With this orientation, the movementof the needle due to the recording of the left channel of the binauralsystem will be in the direction of arrow 17 while the movement of theneedle due to the recording of the right channel of the binaural systemwill be in the direction of arrow 18. Since the arrows 17 and 18 are atright angles to each other, the needle can follow independently therecording in each channel.

Any opposite pair of electrodes, for example the electrodes 8 and 10,are grounded. The output of the right channel then appears betweenelectrode 9 and ground and is due to the polarization in the directionsindicated by the arrows 13 and 14. The polarization indicated by thearrows 15 and 16 produces no output for the right channel because thevoltages generated by the needle excursions from the right channelrecording are equal and opposite. The left channel output appearsbetween electrode 7 and ground and is due to the polarization indicatedby the arrows 15 and 16. No output for the left channel is obtained fromthe polarization due to the arrows 13 and 14 because the voltagesgenerated by the needle excursions from the left channel are equal andopposite.

To reconstitute the sound, the output from the right channel is fedthrough amplifier 19 to speaker 20 while the output from the leftchannel is fed through amplifier 21 to speaker 22. The speakers 20 and22 are so located that the sound reproduces the input from the binauralmicrophones used in recording the record.

For perfect reproduction, it is necessary that the ceramic bar beaccurately made, accurately oriented, and accurately polarized. Accuracyin manufacture insures the equality of the deflection characteristicsabout axes 11 and 12 so that equal forces from the needle produce equaldeflections about these axes. Accuracy of polarization insures equalityof output due to the polarization indicated by the arrows 13-16inclusive so that the output for the right channel due to thepolarization indicated by arrows 13 and .14 will (for equal needleexcursions) be the same as that obtained in the left channel due to thepolarization indicated by arrows 15 and 16. Furthermore, the equality inpolarization results in com plete cancellation of output in the rightchannel due to the polarization indicated by arrows 15 and 16 andlikewise results in complete cancellation of the output in the leftchannel due to the polarization indicated by arrows 13 and 14.Inaccuracy in orienting the needle with reference to the record surfaceresults in a component of movement in one of the channels appearing asan out: put in the other channel. Inaccuracy in all of these factorsresults in interchannel cross talk which should be kept to a reasonableminimum. Some of the errors in manufacturing may tend to cancel eachother. It is also possibleby changing the orientation of the needle 5 tointroduce a compensating error which may be helpful in minimizing theinterchannel cross talk due to other causes.

The pickup handles the binaural channels independently both'as toelectrical and as to mechanical forces. The outputs for the channelsappear in separate electrodes on opposite sides of the element and arepartially shielded from each other by the grounding of the intermediatepair of electrodes.

. Fig. 5 is a circuit diagram showing another pickup having the binauralchannel outputs each appearing between a single electrode and ground.The pickup element is a bar of polarizable material such as bariumtitanate ceramic having four longitudinally extending electrodes 28, 29,30 and 31 spaced 90 degrees from each other. In a preferred form theelectrodes are arranged between adjacent ribs or flanges 32, 33, 34 and35 with electrode 28 between flanges 32, 33, electrode 29 between'fianges 33, 34, electrode 30 between flanges 34, 35 and electrode 31between flanges 35, 32. The bar is polarized by a field betweenelectrodes 28, 30 and electrodes 29, 31 producing the polarizationindicated by arrows 36, 37, 38 and 39.

The piezoelectric element is assembled, for example as shown in Fig. l,oriented so that the needle 5 is centered directly below one of theelectrodes, for example the electrode 30, and the adjacent flanges orribs 34, 35 are inclined at an angle of 45 degrees with respect to therecord surface. the needle 5 by the recording of the left channel exertsa force in the direction of arrow 17 and causes bending of thepiezoelectric element about axis 40 which extends along the center lineof flanges or ribs 33, 35. Because the axis 40 is at the neutral axis ofthe piezoelectric element, no output is produced by the polarization inthe direction of arrows 37 and 38 except that due to irregularities inthe ceramic or in the application of the clectrodes or the degree ofpolarization. In this connection it should be noted that thepolarization indicated by arrows 37 and 38 are opposite to each other sothat such output as might exist due to the irregularities would tend tocancel. A force in the direction of arrow 17 produces a tension stressin rib 34 and a compression stress in rib 32. This produces a voltagebetween electrode 29 and ground electrode 30 and produces a voltage ofthe same sign and magnitude from electrode 28 to electrode 31. Electrode31 accordingly by reason of the voltage generated due to thepolarization of arrow 36 tends to Z3. direction of arrow 18 does notproduce any output due to the polarization in the direction of arrows36, 39 except that due to irregularity-in the ceramic or the electrodesor the polarization. The force in the direction of arrow 18 produces atension stress in the rib and a compression stress in the rib 33. Thetension stress in the rib 35 causes a voltage to be generated due to thepolarization in the direction of arrow 38 between electrode 31 andground electrode 30. V This voltage is fed to the right channelamplifier l9 and right channel speaker 2h; The stress in the directionof arrow 18 produces a voltage between electrodes 28 and 29 of the samemagnitude and sign as the voltage between electrodes 31 and 30. That is,electrode 29 assumes the same polarity as ground'electrode 3t) andelectrode 28 assumes the same polarity as electrode 31. This means thatby reason of the voltage generated by a force in the direction of arrow18, no voltage is fed to the left channel amplifier 21. i

The Fig. 5 pickup has very low interchannel cross talk because a voltageproduced by the recording in one channel which normally would beelectrostatically coupled to the other channel is opposed by an equaland opposite voltage generated by the same stress in the other channel.The result is that when the needle is following a recording for only oneof the channels, an output is generated in the output electrode for thatchannel while the output electrode for the other channel in which thereis no recording remains at ground potential. The Fig. 5 pickup has theadvantage of having its output forboth channels between a singleelectrode and ground. This is the conventional single ended output incommon use in the phonograph industry. The pickup accordingly can bereadily substituted in existing phonographs.

When so mounted, excursion of p When either the top or bottom electrodes28, 30 in Fig. 5 is grounded, the voltages appearing on the outputelectrodes 29, 31 due to a vertical force on the needle 5 are in phasewith each other. When either the left or right electrodes 29, 31 in Fig.5 is grounded, the voltages appearing on the output electrode 28, 30 dueto a vertical force on the needle 5 such as caused by turntable rumbleare out of phase with each other and may be trapped in a filterconnected across the channel output electrodes. When any one of the fourelectrodes is grounded, the adjacent electrodes may be used as outputelectrodes respectively for the left and right channels. For example, ifthe electrode 35 is grounded, the left and right channel outputs willthen appear respectively on electrodes 29 and 31. Similar analyses maybe made for the grounding of any other electrode. Rumble may also bereduced when either the top or bottom electrode (28 or 30) is groundedby connecting a low pass filter from ground tothe one not grounded. Theforegoing assume the same potential as ground electrode 30. This 7 meansthat the force due to the recording of the left channel as indicated byarrow 17 produces an output at electrode 29 which is fed through theamplifier 21 and speaker 22 as in Fig. 4. The voltage appearing onelectrode 29 does not appear on the right channel elecr trode 31 andaccordingly does not produce any output in the right channel speaker 20.The recording due to the right channel produces a force on the needle 5in the direction of arrow 18 and causes bending of the piezoelectricelement about the axis 41 which extendsalong the center line of flangesor ribs 32, 34 or along the neutral axis of the piezoelectric element.The force in the disclosure for reduction of rumble is being claimed inapplication Serial No. 737,574, filed May 26, 1958.

What is claimed as new is:

l. A'piezoelectric element having separate outputs respectively inresponse to bending in about one and the other of two axes substantiallyat right angles to each other, comprising a bar of polarizable ceramichaving two pairs of longitudinally extending electrodes, with theelectrodes of each pair on opposite sides of the bar and with therespective pairs arranged on a different one of one of said axes, saidbar being polarized from one electrode of oneof the pairs in divergentdirections to an adjacent electrode of the other pair, one'of thedirections of polarization extending directly from said one electrode tosaid adjacent electrode, the other direction of polariza-' tionextending serially from said one electrode through the remainingelectrodes to said adjacent electrode, one of the pairs of electrodesgrounded, and the outputfor bending about one and the other ofsaid axesappearing respectively between ground and-one and the other of theremaining two electrodes.

2; A phonograph pickupforbinaural records having two channels cut in asingle record groove in two directions at right angles to each othercomprising a bar supported at one end and having a needle coupled to theother end for bending the bar about axes substantially at right anglesto said two directions, said bar being of polarizable ceramic having twopairs of longitudinally extending electrodes, with the electrode of eachpair on opposite sides of a different one of one of said axes, said barbeing polarized from one electrode of one of the pairs in divergentdirections to an adjacent electrode of the other pair, one of thedirections of polarization extending directly from said one electrode tosaid adjacent electrode, the other direction of polarization extendingserially from said one electrode through the remaining electrodes tosaid adjacent electrode, one of the pairs of electrodes grounded, andthe output for bending about one and the other of said axes appearingrespectively between ground and one and the other of the remaining twoelectrodes.

3. The piezoelectric element of claim 1 in which the bar has fourlongitudinal flanges so it is of cross shape in transverse section andthe electrodes are between adjacent flanges.

4. The piezoelectric element of claim 1 in which the bar has equalstiffness in all radial directions.

5. A piezoelectric element having separate outputs respectively inresponse to bending about one and the other of two axes substantially atright angles to each other, said element comprising a bar-like body ofpolarizable ceramic having a pair of electrodes centered on one of theaxes and spaced on opposite sides of the other of the axes, a secondpair of electrodes centered on said other axis and spaced on oppositesides of the first axis, said body being polarized on one side of thefirst axis from one of the electrodes of the second pair in divergingdirections respectively to one and the other of the electrodes of thefirst pair, and said body being polarized on the other side of the firstaxis from one electrode of the first pair to the other electrode of thesecond pair and thence to the other electrode of the first pair.

6. A piezoelectric element comprising a bar-like body of polarizableceramic having four longitudinally extending electrodes symmetricallyspaced about the longitudinal axis of the element in diametricallyopposed pairs centered on axes substantially 90 degrees from each other,said bar being polarized by a field from one pair of electrodes to theother pair of electrodes, means applying forces to said element in twodirections at right angles to each other to cause bending about axes atright angles to each other and at 45 degrees to the axes on which therespective pairs of electrodes are centered, means for grounding oneelectrode, means for connecting one of the electrodes adjacent thegrounded electrode to an output for bending of the bar in one of saidtwo directions, means for connecting the other of the electrodesadjacent the grounded electrode to another out put for bending of thebar in the other of said two directions, whereby cross talk between saidoutputs is reduced.

7. A phonograph pickup for binaural records having two channels cut in asingle record groove in two directions at right angles to each othercomprising a bar supported at one end and having a needle coupled to theother end for bending the bar about axes at right angles to said twodirections, said bar having four symmetrically spaced longitudinallyextending ribs with two pairs of diametrically opposed ribs respectivelysubstantially centered on one and the other of said axes, fourelectrodes symmetrically spaced about the longitudinal axis of the barwith each electrode between adjacent ribs, said bar being of polarizableceramic and polarized by a field from two diametrically opposedelectrodes to the other two electrodes, means for grounding oneelectrode, means for connecting one of the electrodes adjacent thegrounded electrode to an output for bending of the bar in one of saidtwo directions, means for connecting the other of the electrodesadjacent the grounded electrode to another output for bending of the barin the other of said two directions, whereby cross talk between saidoutputs is reduced.

8. A phonograph pickup for binaural records having two channels cut in asingle record groove respectively in two directions at right angles toeach other and at 45 degrees to the record surface comprising a barsupported at one end and having a needle coupled to the other end forbending the bar about two axes at right angles to said two directions,said bar having four longitudinally extending radial ribs spacedsubstantially degrees from each other with diametrically opposite pairsof ribs centered on one and the other of said two axes, four electrodeson the bar spaced 90 degrees from each other with two electrodescentered on an axis perpendicular to the record surface and the othertwo electrodes centered on an axis parallel to the record surface, saidbar being of polarizable ceramic and polarized by a field from saidfirst two electrodes to said other two electrodes, means for groundingone electrode, means for connecting one of the electrodes adjacent thegrounded electrode to an output for bending of the bar in one of saidtwo directions, means for connecting the other of the electrodesadjacent the grounded electrode to another output for bending of the barin the other of said two directions, whereby cross talk between saidoutputs is reduced.

9. A phonograph pickup for binaural records having two channels cut in asingle record groove respectively in two directions at right angles toeach other and at 45 degrees to the record surface comprising a barsupported at one end and having a needle coupled to the other end forbending the bar about two axes at right angles to said two directions,four electrodes on the bar spaced substantially 90 degrees from eachother with two electrodes centered on an axis perpendicular to therecord surface and the other two electrodes centered on an axis parallelto the record surface, said bar being of polarizable ceramic andpolarized by a field from said first two electrodes to said other twoelectrodes, means for grounding one electrode, means for connecting oneof the electrodes adjacent the grounded electrode to an output forbending of the bar in one of said two directions, means for connectingthe other of the electrodes adjacent the grounded electrode to anotheroutput for bending of the bar in the other of said two directions,whereby cross talk between said outputs is reduced.

References Cited in the file of this patent UNlTED STATES PATENTS 2,439,499

